Antenna diversity has long been utilized in wireless communication systems and is currently being deployed in hand-held devices such as cellular telephones.
Many RF Transmitter/receiver systems contain antenna systems which have multiple antennas. The multiple “diversity” antennas are physically separated with the intent that each antenna has a unique coverage pattern.
When an RF transmission is sent to the diversity antenna system, the RF receiver antenna control hardware dynamically determines which antenna contains the best/strongest signal and electrically connects the best antenna to the radio receiver hardware. This dynamic selection can (and usually does) occur independently on each packet/message received on the diversity antenna system.
When selecting a transmit antenna the following assumptions are made:                1. The receive coverage pattern is similar to the transmit coverage pattern for a given antenna in a multiple antenna system, and        2. Adjacent packets in time (e.g., just before or just after one another) tend to be going to or coming from the same far-end node        
The transmit antenna selection algorithm for the diversity antenna system is to use the same antenna which was last selected as the best receive antenna on the most recently received RF packet/message.
However, in many cases one or both of the above-stated assumptions are not valid. In those cases existing systems could select the antenna with the weaker signal response when transmitting to a node.
Accordingly, devices that could take advantage of the availability of multiple antennas during transmission would provide substantial improvement in device performance.